1. Field of the Invention
The invention relates to an oil control valve and a hydraulic control apparatus.
2. Description of Related Art
For higher fuel economies, higher outputs, and so on, internal combustion engines for vehicles (e.g., automobiles) which have a hydraulic variable valve timing mechanism (an example of “hydraulic device”) used for variably controlling the operation timing of engine valves (intake valves and/or exhaust valves) are now in practical use. In such internal combustion engines, a moveable member fixed at one end of the camshaft is driven through oil feeding to and oil drainage from the variable valve timing mechanism, whereby the rotational phase of the camshaft relative to the crankshaft shifts. Thus, by shifting the rotational phase of the camshaft relative to the crankshaft, the operation timing of the valves of the internal combustion engine is variably controlled.
Oil feeding and oil drainage for a hydraulic device, such as the variable valve timing mechanism described above, are performed through a plurality of oil passages constituting a hydraulic circuit connecting the hydraulic device to an oil pump. In such a hydraulic circuit, an oil control valve that is driven by an actuator to change the state of oil feeding to the hydraulic device through the oil passages and the state of oil drainage from the hydraulic device through the oil passages (will hereinafter be collectively referred to as “the state of oil feeding-drainage” where necessary) is provided midway in the oil passages, and the state of oil feeding-drainage for the hydraulic device is changed by driving the oil control valve using the actuator. In this way, the hydraulic device operates hydraulically. It is to be noted that the oil control valve and the actuator together serve as a hydraulic control apparatus for controlling the oil pressure applied to the hydraulic device to drive the hydraulic device.
As an oil control valve for such a hydraulic control apparatus, for example, the one described in Japanese Patent Application Publication No. 2010-127252 may be used. The oil control valve described in Japanese Patent Application Publication No. 2010-127252 includes a housing having a plurality of ports connectable to the respective oil passages and an elongated spool disposed in the housing. The state of oil feeding-drainage for the hydraulic device is changed by changing the state of connections between the respective ports of the housing by adjusting the axial position of the spool.
Further, an oil control valve is known in which a drain passage for draining the oil that has entered a housing from a hydraulic device is formed in a spool such that the same passage extends in the axial direction of the spool. Such a drain passage in a spool is provided to, for example, obtain a larger passage area for improving the efficiency of oil drainage through the drain passage, and secure a region where the drain passage is formed. It is to be noted that such an oil control valve is driven by the spool being axially moved under the pressure applied to the axial end face of the spool from the actuator. In such a case, the outlet of the drain passage, which is formed in the spool as mentioned above, cannot be provided at the axial end face of the spool, and thus it is provided at a radial side face of the axial end portion of the spool.
Meanwhile, in the above-described structure in which the drain passage extending in the axial direction of the spool is formed in the spool of the oil control valve and the outlet of the drain passage is provided at the radial side face of the axial end portion of the spool, inevitably, the internal structure of the axial end portion of the spool is complicated, and therefore there is a possibility of an increase in the time and effort required for fabricating the inside of the axial end portion of the spool, resulting in an increase in the manufacturing cost.